Preparation of transition metal nanoparticles and surfaces modified with (CO)polymers synthesized by RAFT

ABSTRACT

A new, facile, general one-phase method of generating thio-functionalized transition metal nanoparticles and surfaces modified by (co)polymers synthesized by the RAFT method is described. The method includes the stops of forming a (co)polymer in aqueous solution using the RAFT methodology, forming a colloidal transition metal precursor solution from an appropriate transition metal; adding the metal precursor solution or surface to the (co)polymer solution, adding a reducing agent into the solution to reduce the metal colloid in situ to produce the stabilized nanoparticles or surface, and isolating the stabilized nanoparticles or surface in a manner such that aggregation is minimized. The functionalized surfaces generated using these methods can further undergo planar surface modifications, such as functionalization with a variety of different chemical groups, expanding their utility and application.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 60/367,816 filed Mar. 27, 2002, the contents ofwhich are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The government may own rights in the present invention pursuant to grantnumber DE-FC26-01BC15317 from the U.S. Department of Energy, and awardnumber DMR-0213883 from the National Science Foundation.

FIELD OF THE INVENTION

The invention relates generally to the production of nanoparticles andsurfaces and, more specifically, to the production of (co)polymermodified transition metal surfaces and nanoparticles. In particular, thepreparation of transition metal nanoparticles and surfaces stabilized ormodified by (co)polymers using the RAFT process in whichthiocarbonylthio compounds act as chain transfer agents is disclosed, aswell as their potential use in, but not limited to, optics, medicine,electronics, biochips, high-throughput screening, and biologicaltransfer agents through further functionalization of the terminal endgroups on the attached polymers. The planar surface modification of the(co)polymer stabilized surfaces of the present disclosure are alsodescribed.

BACKGROUND OF THE INVENTION

Nanoparticles are of particular interest because of their use ascatalysts, photocatalysts, adsorbents, sensors, ferrofluids, and due totheir applications in optical, electronic, and magnetic devices. Sincethe characteristics imparted by the nanoparticles are dependant to agreat part on the method of preparation, the synthesis of thenanoparticles can be critical.

Thiol-stabilized nanoparticles, in particular gold nanoparticles(Au-NPS), have been the focus of intense interest lately due to theirpotential use in the fields of optics, immunodiagnostics, andelectronics. There exist a number of examples of small moleculestabilization using alkanethiols on a variety of metal species,including gold and palladium.

Recently, research has been directed to the application of synthetic(co)polymers as stabilization species for metal nanoparticles, such asstable gold colloids prepared by in-situ reduction (Mayer, A. B. R.,Eur. Polym. Journal 1998, 34, 103–108); ATR grafting from polymerizationto attach polymer chains to gold nanoparticles (Nu, S., et al. Angew.Chem. Int. Ed. 2001, 40, 4016–4018); gold nanoparticles decorated withcovalently bound thiol-capped polystyrene macromolecules (Corbierre, M.K, et al. J. Am. Chem. Soc. 2001, 123, 10411–10412); and platinumnanoparticles with long perfluorinated carbon chains (Moreno-Mañas, M.,et al. Chem. Commun. 2002, 60–61). However, these examples use processesof “grafting-to” and “grafting-from” for nanoparticle stabilization thatutilize living polymerization techniques and suffer from disadvantagessuch as special reaction conditions, sensitivity to specific monomers,and necessitate expensive reagents and/or monomers.

Additional research in the area of nanoparticle synthesis has focused onthe development of “pseudo-living” polymerization methods. Threeprincipal approaches have been described to achieve this pseudo-livingfree-radical polymerization technique; reversible termination,reversible termination by ligand-transfer, and degenerative chaintransfer. The first of these, typically referred to asnitroxide-mediated or stable free-radical polymerization (SFRP) has beenexploited in the synthesis of controlled styrenic-based (co)polymers(Solomon, D. H., et al. U.S. Pat. No. 4,581,429; Goto, A.; et al.Macromolecules 1996, 29, 3050; Yoshida, E., et al. J. Polym. Sci., PartA: Polym. Chem. 1997, 35, 2371).

Subsequently, several groups disclosed an atom transfer radicalpolymerization (ATRP) process, which is a radical polymerization withreversible termination by ligand transfer to a metal complex. Thistechnique has been shown to work especially well with styrenic andacrylate-based polymer monomers, similar to SFRP (Wang, J.-S., et al.Macromolecules 1995, 28, 7572; Sawamoto, M., et al., Trends Polym. Sci.1996, 4, 371; Bandts, J. A. M., et al. J. Organomet. Chem. 1999, 584,246).

Most recently, a third mechanism has been proposed for achieving“pseudo-living” polymerization character, which is a free-radicalpolymerization with reversible chain transfer (also termed degenerativechain transfer). It has been termed RAFT—reversibleaddition-fragmentation chain transfer polymerization (Le, T. P., et al.,WO Patent 9801478; Chiefari, J., et al. Macromolecules 1998, 31,5559–5562; Moad, G., et al. Polym. Int. 2000, 49, 993). This techniqueappears to offer several advantages over the previous ATRP and SFKPtechniques, in that a vast array of monomers can be used, and thereaction can be performed under a broad range of experimental conditionsusing a variety of solvents.

Despite these recent advances, few methods have been described whichallow for the covalent attachment of polymer chains directly totransition metal colloids or surfaces (the so-called grafting-toapproach), as opposed to simple physical adsorption of a (co)polymer.Thus, there exists a need for a new, facile manner for the preparationof (co)polymer stabilized transition metal nanoparticles and surfaces.The approach described herein takes advantage of the method of polymersynthesis in which the polymers produced bear thiocarbonylthio endgroups which can be reduced in situ in the presence of a transitionmetal sol or surface, yielding a polymer with a thiolate end-group whichcovalently bonds to the metal colloid or metal surface. This fast,facile, “one-step” synthetic procedure of simultaneous reduction of thepolymer end-group and the metal colloid or surface in situ issignificantly less demanding than the grafting-from approach whichrequires initial modification of the metal colloid with a suitablepolymerization initiator, followed by subsequent polymerization. Thisnew, rapid one-step method allows for the preparation of polymerssuitable for covalent attachment on an industrial scale.

SUMMARY OF THE INVENTION

The present invention relates to a novel, inexpensive and convenientprocess for the preparation of transition metal nanoparticles andsurfaces which are modified by (co)polymers synthesized using the RAFTtechnique.

More specifically, a facile method of preparing transition metalnanoparticles and surfaces stabilized or modified by (co)polymerssynthesized using the RAFT technique includes the steps of: forming adithio end-capped (co)polymer by reacting at least one polymerizablemonomer or co-monomer with a free radical source and a chain transferagent, such as a dithioester, using the RAFT method in a solvent;forming a metal precursor colloidal solution from a transition metal ina solvent; introducing the metal precursor colloidal solution to thedithio end-capped (co)polymer, in an open-atmosphere setup; adding areducing agent into the solution to reduce the metal colloidal salt orsol and the thiocarbonylthio compound in situ in order to produce thenanoparticles; mixing the solution for a period of time sufficient tostabilize the nanoparticles; concentrating the stabilized nanoparticlesand separating the by-products by centrifugation; and concentrating thestabilized nanoparticles in a manner such that aggregation is minimized.

Further, within the invention, preferably transition metal nanoparticlesor surfaces are stabilized or modified by a (co)polymer which iscationic, anionic, non-ionic, or zwitterionic in a aqueous or partiallyaqueous solution or emulsion. The precursor colloidal solution can beintroduced to the dithio end-capped (co)polymer in an open atmosphereenvironment.

A facile method of preparing transition metal surfaces modified by(co)polymers synthesized using the RAFT technique for use in formingpolymer-modified transition metal films and surfaces is also described,including the steps of: forming a dithio end-capped (co)polymer byreacting at least one polymerizable monomer or co-monomer with a freeradical source and a chain transfer agent, such as a dithioester, usingthe RAFT method in a solvent; introducing a metal surface to the dithioend-capped (co)polymer solution; adding a reducing agent into thesolution to reduce the metal surface (colloid, film, etc) and thethiocarbonylthio compound in situ; and allowing the solution and metalsurface to remain in contact for a period of time sufficient tostabilize the transition metal surface.

Additionally, in forming the polymer-modified transition metal films andsurfaces, the isolation of the slide/surface also includes the steps ofremoving the polymer-modified transition metal surface from the solutionin order to separate the by-products from the synthesis; adding asolvent, such as water, to the face of the slide/surface in order torinse the stabilized surface; and optionally drying the (co)polymerstabilized surface in a manner such that aggregation of thenanoparticles is minimized.

The above-mentioned innovations may be employed individually, or incombination, to control the composition and performance of thenanoparticles or surfaces formed.

DEFINITIONS

The following definitions are provided in order to aid those skilled inthe art in understanding the detailed description of the presentinvention.

“Chain transfer agents” (CTA) as used herein refer to those compoundsuseful in polymeric reactions having the ability to add monomer units tocontinue a polymerization process.

“Free-radical initiators” (initiators) as used herein refer to a speciescomprising any of the large number of organic compounds with a labilegroup which can be readily broken by heat or irradiation (UV, gamma,etc.) and have the ability to initiate free radical chain reactions.

“Monomer” as used herein means a polymerizable allylic, vinylic, oracrylic compound which may be anionic, cationic, non-ionic, orzwitterionic.

“Anionic copolymers” as used herein, refer to those (co)polymers whichpossess a net negative charge.

“Anionic monomer” as defined herein refers to a monomer which possessesa net negative charge. Representative examples of anionic monomersinclude metal salts of acrylic acid, sulfopropyl acrylate, methacrylate,or other water-soluble forms of these or other polymerizable carboxylicacids or sulphonic acids, and the like.

“Cationic (co)polymers”, as defined herein, refer to those (co)polymerswhich possess a net positive charge.

“Cationic monomers”, as defined herein, refer to those monomers whichpossess a net positive charge. Representative cationic monomers includethe quaternary salts of dialkylaminoalkyl acrylates and methacrylates,N,N-diallydialkyl ammonium halides (such as DADMAC),N,N-dimethylaminoethylacrylate methyl chloride quaternary salt, and thelike.

“Neutral” or “non-ionic (co)polymers”, as defined herein, refer to those(co)polymers which are electrically neutral and possess no net charge.

“Nonionic monomers” are defined herein to mean a monomer which iselectrically neutral. Representative nonionic or neutral monomers areacrylamide, N-methylacrylamide, N,N-dimethyl(meth)acrylamide,N-methylolacrylamide, N-vinylformamide, and N,N-dimethylacrylamide, aswell as hydrophilic monomers such as ethylene glycol methyacrylate,diols, triols, and the like.

“Betaine”, as used herein, refers to a general class of salt compounds,especially zwitterionic compounds, and include polybetaines.Representative examples of betaines which can be used with the presentinvention include:N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine,N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine,N,N-dimethyl-N-acrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine,N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine,2-(methylthio)ethyl methacryloyl-S-(sulfopropyl)-sulfonium betaine,2-[(2-acryloylethyl)dimethylammonio]ethyl 2-methyl phosphate,2-(acryloyloxyethyl)-2′-(trimethylammonium)ethyl phosphate,[(2-acryloylethyl)dimethylammonio]methyl phosphonic acid,2-methacryloyloxyethyl phosphorylcholine (MPC),2-[(3-acrylamidopropyl)dimethylammonio]ethyl 2′-isopropyl phosphate(AAPI), 1-vinyl-3-(3-sulfopropyl)imidazolium hydroxide,(2-acryloxyethyl)carboxymethyl methylsulfonium chloride,1-(3-sulfopropyl)-2-vinylpyridinium betaine,N-(4-sulfobutyl)-N-methyl-N,N-diallylamine ammonium betaine (MDABS),N,N-diallyl-N-methyl-N-(2-sulfoethyl)ammonium betaine, and the like.

“Zwitterionic”, as defined herein, refers to a molecule containing bothcationic and anionic substituents or electronic charges. Such moleculescan have a net neutral overall charge, or can have a net positive or netnegative overall electronic charge.

“Zwitterionic (co)polymers”, as defined herein, refer to (co)polymersderived from a zwitterionic monomer, a combination of anionic andcationic charged monomers or those derived from a zwitterionic monomer,including betaines, together with a component or components derived fromother betaine monomers, ionic monomers, and non-ionic monomer(s), suchas a hydrophobic and/or hydrophilic monomer. Suitable hydrophobic,hydrophilic, and betaine monomers are any of those known in the art.Representative zwitterionic co(polymers) include homopolymers,terpolymers, and (co)polymers. In polybetaines, all the polymer chainsand segments within those chains are necessarily electrically neutral.As a result, polybetaines represent a subset of polyzwitterions,necessarily maintaining charge neutrality across all polymer chains andsegments due to both anionic charge and cationic charge being introducedwithin the same monomer (see, for example, Lowe A. B., et al., ChemicalReviews 2002, Vol. 102, pp. 4177–4189, which is incorporated herein byreference).

“Zwitterionic monomer” means a polymerizable molecule containingcationic and anionic (thus, charged) functionalities in equalproportions, such that the molecule is typically, but not always,electronically neutral overall. Those monomers containing charges on thesame monomer are termed “polybetaines.”

“Transition metal complex”, or “transition metal sol”, as definedherein, refers to a metal colloid solution/complex, wherein the metal isany of the metals comprising the d-block section of the Periodic Tableof Elements that, as elements, have partly filled d shells in any oftheir commonly occurring oxidation states, constituting those elementsin the first, second and third transition series, as defined by IUPAC.

“Living polymerization”, as used herein, refers to a process whichproceeds by a mechanism whereby most chains continue to grow throughoutthe polymerization process, and where further addition of monomerresults in continued polymerization. The molecular weight is controlledby the stoichiometry of the reaction.

“Radical leaving group” refers to a group attached by a bond that iscapable of undergoing homolytic scission during a reaction, therebyforming a radical.

“Stabilized” refers to the transition-metal-stabilized nanoparticles ofthe present invention, and refers to the ability of the colloids toresist aggregation for several weeks after preparation under an airatmosphere.

“Surface”, as used herein, refers to the exterior, external, upper, orouter boundary of an object or body, and is meant to include a plane orcurved two-dimensional locus of points as the boundary of athree-dimensional region, e.g. a plane.

“GPC number average molecular weight”, (Mn) means a number averagemolecular weight, determined by Aqueous Size Exclusion Chromatography(ASEC).

“GPC weight average molecular weight”, (Mw) means a weight averagemolecular weight measured by utilizing gel permeation chromatography.

“Polydispersity” (Mw/Mn) means the value of the GPC weight averagemolecular weight divided by the GPC number average molecular weight.

Unless specified otherwise, alkyl groups referred to in thisspecification can be branched or unbranched and contain from 1 to 20carbon atoms. Alkenyl groups can similarly be branched or unbranched,and contain from 2 to 20 carbon atoms. Saturated or unsaturatedcarbocyclic or heterocyclic rings can contain from 3 to 20 carbon atoms.Aromatic carbocyclic or heterocyclic rings can contain from 5 to 20carbon atoms.

“Substituted”, as used herein, means that a group can be substitutedwith one or more groups that are independently selected from the groupconsisting of alkyl, aryl, epoxy, hydroxy, alkoxy, oxo, acyl, acyloxy,carboxy, carboxylate, sulfonic acid, sulfonate, alkoxy- oraryloxy-carbonyl, isocyanato, cyano, silyl, halo, dialkylamino, andamido. All substituents are chosen such that there is no substantialadverse interaction under the conditions of the experiments.

DETAILED DESCRIPTION OF THE INVENTION

Generally, the present disclosure describes an inexpensive and efficientprocess for preparing transition metal nanoparticles or other suitablesurfaces modified by (co)polymers prepared using the RAFT process. Thisis shown generally in schemes 1 and 2 below. As described in detailherein, and as illustrated in scheme 1, the nanoparticles of theinvention are synthesized by the reaction of a transition metal complex,such as a metal salt, colloid, or sol, with thiocarbonylthio compoundsin aqueous solution, in the presence of a reducing agent. According tothis aspect of the present disclosure, the methods describedsimultaneously reduce the metal salt (or sol) and the thiocarbonylthiogroup to a thiol in one step, in situ. The structuro-terminal end-groups(X) of the thus-anchored (co)polymers of this invention could act asactive end groups in numerous applications, allowing for a variety ofchemistries to be performed, such as the chemical modification of theterminal end-group.

A further embodiment of the present disclosure is illustrated in scheme2, wherein surfaces such as films, metals, and the like are reacted withthiocarbonylthio compounds or other CTAs in aqueous solution, in thepresence of at least one reducing agent. Similar to the processdescribed for use with nanoparticles, the thiocarbonylthio compounds arereduced to thiols in situ, causing the surfaces to be modified, and thestructuro-terminal end groups, X, can be further functionalized in avariety of manners.

As alluded to above, it is further envisioned that thestructuro-terminal end-groups (X) of the thus-anchored (co)polymers ofthis invention could act as active end groups in numerous applications,allowing for a variety of functionalities to be attached to thesegroups. Functional groups which can be anchored to surfaces andnanoparticles via (co)polymers according to the present inventioninclude, but are not limited to, amines (primary, secondary, andtertiary), amides, carbonyls, nitroso compounds, halides, alcohols,carboxylic acids and their associated salts, esters, anhydrides, andacid halides.

By way of example only, compounds which could be anchored to a carbonylend group of the anchored polymeric chain would include, but are notlimited to, DNA, RNA, DNA and RNA sequences, nucleotides,oligonucleotides, recombinant oligonucleotides, nucleosides,saccharides, polysaccharides, proteins, glycoproteins, lipoproteins,lipids, alcohols, steroids, peptides including recombinant proteins andpolypeptides, amino acids (natural, non-natural, and synthetic),lectins, enzymes, PNAs, peptoids, glycosphingolipids, and hormones. Forexample, thiol groups could be introduced into the system by way of afree carboxylic acid end group by coupling an amino acid such ascysteine (or derivatives thereof) using standard amide bond formingtechniques (e.g., peptide bond formation using carbodiimide chemistry).

Methods of attachment to the functionalized end-groups would include anyof the methods known in the art for performing such chemistry, which maybe either by traditional solution phase synthesis methods or by solidphase synthesis methods, in an automated or non-automated fashion.Examples of such methods for synthesis are described in M. Bodanszky,Principles of Peptide Synthesis, 2^(nd) Ed., Springer-Verlag, Berlin,1993; J. Jones, Amino Acid and Peptide Synthesis, Oxford UniversityPress, New York, 1997; and B. Bunin, The Combinatorial Index, AcademicPress, San Diego, 1998. Such methods would include but are not limitedto amide bond forming reactions using active esters, azides, enzymes,N-carboxyanhydrides, active ester methods, carbodiimide reagents andmethods, methods using Woodward reagent K, carboduimidazole methods,oxidation-reduction methods, acyl halides, anhydrides (symmetrical andmixed), methods using phosphonium and uronium reagents such as BOP,HBTU, TBTU, and PyBrOP, and other methods which would be obvious to oneof skill in the art.

Illustrative of the methods useful for attaching DNA segments, RNAsegments, and bridging or non-bridging nucleotides to the nanoparticlesand surfaces of this invention are solution-phase synthesis, solid-phasesynthesis, automated solid-phase synthesis, automated solution-phasesynthesis, phosphoramidite chemistry, phosphorothioamidite chemistriy,hydrogen-phosphonate methods, and other known methods of oligonucleotidesynthesis as shown in the following references, which are herebyincorporated by reference: U.S. Pat. Nos. 4,458,066, 4,500,707; J. Am.Chem. Soc. 1981, 3185–3191; Jones, Chapter 2, and Atkinson, et al.,Chapter 3, in Gait, ed., Oligonucloetide Synthesis: A Practical Approach(1984); Brill, et al. J. Am. Chem. Soc. 1989, 2321; and Froehler, et al.Nucleic Acids Res. 1986, 5399–5407. Furthermore, less-common modes ofincorporation, such as enzymatic (Bioorg. Khim. 1987, 13, 1045–52) andmethods of producing sulfurized oligonucleotide analogs (Nucleosides &Nucleotides 1989, 967–68); (Tetrahedron Letters 1986, 5575–5578);(Tetrahedron Letters 1991, 3005–3008) are also envisioned using thenanoparticles of this invention.

While not wishing to be bound to any one particular mechanism, it isbelieved that RAFT polymerizations with a singly-functional chaintransfer agent (CTA), such as a dithioester, occur by the mechanismillustrated in scheme 3. Briefly, an initiator produces a free radical,which subsequently reacts with a polymerizable monomer. The monomerradical reacts with other monomers and propagates to form a chain, P_(n)^(•), which can react with a CTA. The CTA can fragment, either formingR^(•), which will react with another monomer that will form a new chain,P_(m) ^(•), or P_(n) ^(•), which will continue to propagate. In theory,the propagation of P_(m) ^(•) and P_(n) ^(•) will continue until nomonomer remains or termination occurs. After the first polymerizationhas finished, in particular circumstances, a second monomer can be addedto the system to form a block copolymer. The present invention can beused to form block copolymers attached to transition-metalnanoparticles.

Suitable polymerization monomers and comonomers of the present inventioninclude, but are not limited to, methyl methacrylate, ethyl acrylate,propyl methacrylate (all isomers), butyl methacrylate (all isomers),2-ethylhexyl methacrylate, isobornyl methacrylate, methacrylic acid,benzyl methacrylate, phenyl methacrylate, methacrylonitrile,alpha-methylstyrene, methyl acrylate, ethyl acrylate, propyl acrylate(all isomers), butyl acrylate (all isomers), 2-ethylhexyl acrylate,isobornyl acrylate, acrylic acid, benzyl acrylate, phenyl acrylate,acrylonitrile, styrene, acrylates and styrenes selected from glycidylmethacrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate(all isomers), hydroxybutyl methacrylate (all isomers),N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate,triethyleneglycol methacrylate, itaconic anhydride, itaconic acid,glycidyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate (allisomers), hydroxybutyl acrylate (all isomers), N,N-dimethylaminoethylacrylate, N,N-diethylaminoacrylate, triethyleneglycol acrylate,methacrylamide, N-methylacrylamide, N,N-dimethylacrylamide,N-tert-butylmethacrylamide, N-n-butylmethacrylamide,N-methylolacrylamide, N-ethylolacrylamide, vinyl benzoic acid (allisomers), diethylaminostyrene (all isomers), alpha-methylvinyl benzoicacid (all isomers), diethylamino alpha-methylstyrene (all isomers),p-vinylbenzenesulfonic acid, p-vinylbenzene sulfonic sodium salt,trimethoxysilylpropyl methacrylate, triethoxysilylpropyl methacrylate,tributoxysilylpropyl methacrylate, dimethoxymethylsilylpropylmethacrylate, diethoxymethylsilylpropyl methacrylate,dibutoxymethylsilylpropyl methacrylate, diisopropyoxymethylsilylpropylmethacrylate, dimethoxysilylpropyl methacrylate, diethoxysilylpropylmethacrylate, dibutoxysilylpropyl methacrylate, diisopropoxysilylpropylmethacrylate, trimethoxysilylpropyl acrylate, triethoxysilylpropylacrylate, tributoxysilylpropyl acrylate, dimethoxymethylsilylpropylacrylate, diethoxymethylsilylpropyl acrylate, dibutoxymethylsilylpropylacrylate, diisopropoxymethylsilylpropyl acrylate, dimethoxysilylpropylacrylate, diethoxysilylpropyl acrylate, dibutoxysilylpropyl acrylate,diisopropoxysilylpropyl acrylate, vinyl acetate, vinyl butyrate, vinylbenzoate, vinyl chloride, vinyl flouride, vinyl bromide, maleicanhydride, N-phenyl maleimide, N-butylmaleimide, N-vinylpyrrolidone,N-vinylcarbazole, betaines, sulfobetaines, carboxybetaines,phosphobetaines, butadiene, isoprene, chloroprene, ethylene, propylene,1,5-hexadienes, 1,4-hexadienes, 1,3-butadienes, and 1,4-pentadienes.

Additional suitable polymerizable monomers and comonomers include, butare not limited to, vinyl acetate, vinyl alcohol, vinylamine,N-alkylvinylamine, allylamine, N-alkylallylamine, diallylamine,N-alkyldiallylamine, alkylenimine, acrylic acids, alkylacrylates,acrylamides, methacrlic acids, maleic anhydride, alkylmethacrylates,methacrylamides, N-alkylacrlamides, N-alkylmethacrylamides, n-vinylformamide, vinyl ethers, vinyl naphthalene, vinyl pyridine, vinylsulfonates, ethylvinylbenzene, aminostyrene, vinylbiphenyl,vinylanisole, vinylimidazolyl, vinylpyridinyl,dimethylaminomethystyrene, trimethylammonium ethyl methacrylate,trimethylammonium ethyl acrylate, dimethylamino propylacrylamide,trimethylammonium ethylacrylate, trimethylammonium ethyl methacrylate,trimethylammonium propyl acrylamide, dodecyl acrylate, octadecylacrylate, and octadecyl methacrylate.

The free-radical polymerization initiators, or free radical source, ofthe present invention are chosen from the initiators conventionally usedin radical polymerization, such as azo-compounds, hydrogen peroxides,redox systems, and reducing sugars. More specifically, the source offree radicals suitable for use with the present invention can also beany suitable method of generating free radicals, including but notlimited to thermally induced homoytic scission of a suitable compound orcompounds (s) [thermal initiators include peroxides, peroxyesters, andazo-compounds], redox initiating systems, photochemical initiatingsystems, or high energy radiation such as electron beam, X-ray, orgamma-ray radiation. The initiating system is chosen such that under thereaction conditions, there is no substantial adverse interaction of theinitiator, the initiator conditions, or the initiating radicals with thetransfer agent under the conditions of the procedure. The initiatorshould also have the requisite solubility in the reaction medium ormonomer mixture.

Thermal initiators are chosen to have an appropriate half-life at thetemperature of polymerization. These initiators can include, but are notlimited to, one or more of 2,2′-azobis(isobutyronitrile),2,2′-azobis(2-cyano-2-butane), dimethyl 2,2′-azobisdimethylisobutyrate,4,4′-azobis(4-cyanopentanoic acid),1,1′-azobis(cyclohexanecarbonitrile), 2-(t-butylazo)-2-cyanopropane,2,2′-azobis[2-methyl-N-(1,1)-bis(hydroxyethyl)]-propionamide,2,2′-azobis(N,N′-dimethyleneisobutylamine),2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide],2,2′-azobis(isobutyramide) dihydrate,2,2′-azobis(2,2,4-trimethylpentane), 2,2′-azobis(2-methylpropane,t-butyl peroxyacetate, t-butyl peroxybenzoate, t-butyl peroxyoctoate,t-butyl peroxyneodecanoate, t-butylperoxy isobutyrate, t-amyperoxypivalate, t-butyl peroxypivalate, di-isopropyl peroxydicarbonate,dicyclohexyl peroxydicarbonate, dicumyl peroxide, dibenzoyl peroxide,dilauroyl peroxide, potassium peroxydisulfate, ammonium peroxydisulfate,di-t-butyl hyponitrite, and dicumyl hyponitrite.

Examples of hydrogen peroxides which may act as free-radical initiatorsaccording to the present disclosure include, but are not limited to,tert-butyl hydroperoxide, cumene hydroperoxide, tert-butylperoxyacetate, lauroyl peroxide, tert-amyl peroxypivalate, tert-butylperoxypivalate, dicumyl peroxide, hydrogen peroxide, Bz₂O₂ (dibenzoylperoxide), potassium persulphate, and ammonium persulphate.

Photochemical initiator systems are chosen to have the requisitesolubility in the reaction medium, monomer mixture, or both, and have anappropriate quantum yield for radical production under the conditions ofthe polymerization. Examples include, but are not limited to, benzoinand benzoin derivatives, benzophenone and benzophenone derivatives, acylphosphine oxides, and photo-redox systems.

Redox initiator systems are chosen to have the requisite solubility inthe reaction medium, monomer mixture, or both, and have an appropriaterate of radical production under the conditions of the specificpolymerization. Such initiating systems suitable for use with thepresent disclosure can include combinations of oxidants such aspotassium peroxydisulfate, hydrogen peroxide, t-butyl hydroperoxide, andreductants such as iron (II), titanium (III), potassium thiosulfite, andpotassium bisulfite. Other suitable initiating systems are described inMoad and Solomon, “The Chemistry of Free Radical Polymerization,”Pergamon, London, 1995; pp. 53–95, which is incorporated herein byreference.

Further examples of redox systems suitable for use with the presentdisclosre include, but are not limited to, mixtures of hydrogen peroxideor alkyl peroxide, peresters, percarbonates, and the like in combinationwith any one of the salts of iron, titaneous salts, zinc salts, zincformaldehyde sulphoxylate, sodium salts, or sodium formaldehydesulphoxylate.

The reactions of the present disclosure (e.g., polymerizations, surfacemodifications/immobilizations, and preparations of polymer-stabilizedmetal colloids or other appropriate surfaces, such as silicon, ceramic,metals, etc.) can be carried out in any suitable solvent or mixturethereof. Suitable solvents include, but are not limited to, water,alcohol (e.g. methanol, ethanol, n-propanol, isopropanol, butanol),tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), dimethylformamide(DMF), acetone, acetonitrile, hexamethylphosphoramide (HMPA), hexane,cyclohexane, benzene, toluene, methylene chloride, ether (e.g. diethylether, butyl ether or methyl tert-butyl ether), methyl ethyl ketone(MEK), chloroform, ethyl acetate, and mixtures thereof. Preferably, thesolvents include water, mixtures of water, or mixtures of water andwater-miscible organic solvents, such as DMF. Most preferably, water isthe solvent.

For heterogeneous polymerization, it is desirable to choose a CTA whichhas appropriate solubility characteristics. For example, for aqueousemulsion polymerization, the CTA should preferably partition in favor ofthe organic (monomer) phase and yet have sufficient aqueous solubilitythat it is able to distribute between the monomer droplet phase and thepolymerization locus.

The chain transfer reagents (CTAs) of the present invention arecompounds, such as dithioester compounds, water-soluble dithioesercompounds, disulphides, xanthate disulphides, thiocarbonylthiocompounds, and dithiocarbamates which react with either the primaryradical or a propagating polymer chain, thereby forming a new CTA andeliminating the R radical, thereby reinitiating polymerization. The CTAsof the present invention are either commercially available, such ascarboxymethyl dithiobenzoate, or readily synthesized using knownprocedures. Examples of CTAs suitable for use in the present inventionare cumyl dithiobenzoate, DTBA (4-cyanopentanoic acid dithiobenzoate),BDB (benzyl dithiobenzoate), CDB (isopropyl cumyl dithiobenzoate), TBP(N,N-dimethyl-s-thiobenzoylthiopropionamide), TBA(N,N-dimethyl-s-thiobenzoylthioacetamide, trithiocarbonates,dithiocarbamates, (phosphoryl)dithioformates and(thiophosphoryl)dithioformates, bis(thioacyl)disulfides, xanthates,dithiocarbonate groups used in MADIX (Macromolecular Design viaInterchange of Xanthate) which are either commercially available,synthesized according to well-established organic synthesis routes, orsynthesized as previously described in U.S. Pat. No. 6,153,705, which ishereby incorporated by reference, and CTPNa (sodium 4-cyanopentanoicacid dithiobenzoate) and related compounds, such as those described inU.S. Pat. No. 6,153,705, and PCT International Application WO 9801478A1, which are herein incorporated by reference.

The choice of polymerization conditions is also important. The reactiontemperature should generally be chosen such that it will influence ratein the desired manner. For example, higher temperatures will typicallyincrease the rate of fragmentation. Conditions should be chosen suchthat the number of chains formed from initiator-derived radicals isminimized to an extent consistent with obtaining an acceptable rate ofpolymerization. The polymerization process of the present invention isperformed under conditions typical of conventional free-radicalpolymerization. Polymerization employing the CTAs described above aresuitably carried out with temperatures in the range of −20° C. to 200°C., preferably in the range of 10° C. to 150° C., and most preferably attemperatures in the range of 10° C. to 80° C.

The pH of a polymerization conducted in an aqueous or semi-aqueoussolution can be varied depending upon the conditions and the reactants.Generally, however, the pH is selected so that the selected dithioesteris stable and grafting of the polymer can occur. Typically, the pH isfrom about 0 to about 9, preferably from about 1 to about 7, and morepreferably from about 2 to about 7. The pH can be adjusted using any ofthe means known in the art.

The surfaces which are suitable for use with the (co)polymers of thepresent invention include, but are not limited to, transition metals ofthe first transition series (titanium, vanadium, chromium, manganese,iron, cobalt, nickel, copper, and zinc), the second transition series(zirconium, molybdenum, technetium, ruthenium, rhodium, palladium,silver, cadmium and indium) and the third transition series (hafnium,tantalum, tungsten, rhenium, osmium, iridium, platinum, and gold), inany form or shape, such as nanoparticles, films, wafers, solids, and thelike; silicon wafers; silicon chips; biochip surfaces; biomimeticmaterials; metals, such as stainless steel; ceramics; carbon materials;polymers such as PTFE and PMMA; and composite materials.

More specifically, representative transition metals suitable for use inthe present invention include, but are not limited to, those transitionmetals in the second and third transition metal series of the d-blockelements, having coordination numbers of at least 4 and at most 6, andeither planar or octahedral geometries. Representative transition metalsols preferred for use in this invention include, but are not limitedto, complexes formed from silver (Ag) and associated salts (e.g.,AgNO₃), gold (Au) and associated salts (e.g., HAuCl₄.4H₂O), ruthenium(Ru) and associated salts (e.g., K₃RuCl₆), osmium (Os) and associatedsalts (e.g., Na₂OsCl₆.H₂O), rhodium (Rh) and its associated salts (e.g.,NaRhCl₆), iridium (Ir) and its associated salts (e.g., Na₂IrCl₆.6H₂O),palladium (Pd) and its associated salts (e.g., Na₂PdCl₆.6H₂O) andplatinum (Pt) and associated salts (e.g., Na₂PtCl₆.6H₂O).

Examples of azo-compounds which may act as free-radical initiatorsaccording to the present invention include, but are not limited to,AIBMe (2,2′-azobis(methyl isobutyrate), AIBN(2,2′-azobis(2-cyanopropane), ACP (4,4′-azobis(4-cyanopentanoic acid),AB (2,2′-azobis(2-methylpropane), 2,2′-azobis(isobutyronitrile),2,2′-azobis(2-butanenitrile),2,2′-azobis[2-methyl-N-(1,1)-bis(hydroxymethyl)-2-hydroxyethyl]propionamide,and 2,2′-azobis(2-amidinopropane)dichloride.

Table 1 shows a summary of the molecular weights and polydispersities ofthe (co)polymers utilized for this study. While any water soluble(co)polymer could be used, the (co)polymers envisioned for use accordingthe present invention are anionic, cationic, neutral, and/orzwitterionic (betaine) species.

TABLE 1 Summary of the molecular characteristic of the RAFT-synthesized(co)polymers employed as stabilizing species. Polymer M_(n) ^(a)M_(w)/M_(n) ^(a) Composition PAMPS (P₁) 17,700^(b) 1.27 — PVBTAC (P₂)10,500^(c) 1.06 — PDMA (P₃) 29,100^(d) 1.18 — P(MAEDAPS-b- 58,700^(b)1.19 35:65^(e) PDMA) (P₄) MAEDAPS:DMA ^(a)As determined by Aqueous SizeExclusion Chromatography (ASEC); ^(b)Reported as PNaSSO₃ equivalents;^(c)Reported as P2VP equivalents; ^(d)Absolute MW as determined byon-line light scattering (Wyatt DAWN EOS Optilab RI detector); ^(e)Asdetermined by ¹H-NMR spectroscopy.

Suitable anionic (co)polymers include PAMPS (poly(sodium2-acrylamido-2-methylpropanesulfonate), PAMBA, and other suitableanionic (co)polymers known in the art. Preparation of such anionic(co)polymers is known in the art, and is herein incorporated byreference (Sumerlin, B., et al. Macromolecules 2001, 34, 6561).

Suitable cationic (co)polymers include PVBTAC(poly(arvinylbenzyl)trimethylammonium chloride), and other relatedcationic (co)polymers which are commercially available or availablethrough known synthetic routes.

Suitable nonionic, or neutral (co)polymers include representative(co)polymers including, but not limited to, PDMA(poly(N,N-dimethylacrylamide), and other related neutral (co)polymerswhich are commercially available or available through known syntheticprocedures.

Suitable zwitterionic (co)polymers include PMAEDAPS-b-PDMA(poly(3-[2-N-methylacrylamido)-ethyl dimethyl ammoniopropanesulfonate-block-N,N-dimethylacrylamide), and other zwitterionic(co)polymers commercially available or available through known syntheticprocedures. Preferably, the zwitterionic (co)polymer useful in thepresent invention comprises a component derived from a zwitterionicmonomer (betaine) together with a component or components derived from ahydrophobic or hydrophilic monomer or a mixture of components derivedfrom hydrophobic and hydrophilic monomers.

Suitable betaines include, but are not limited to, ammoniumcarboxylates, ammonium phosphates, and ammonium sulphonates. Particularzwitterionic monomers which can be utilized areN-(3-sulphopropyl)-N-methylacryloxyethyl-N,N-dimethyl ammonium betaine,and N-(3-sulphopropyl)-N-allyl-N,N-dimethyl ammonium betaine.

The dithioester-end capped (co)polymers used in the present inventionwere synthesized using a controlled synthesis in aqueous media,employing any number of chain-transfer agents, most preferably adithiobenzoate or related compound as described above, and a freeradical initiator. The RAFT processes of the present invention can becarried out in aqueous media, in bulk, solution, emulsion,microemulsion, mini-emulsion, inverse emulsion, inverse microemulsion,or suspension, in either a batch, semi-batch, continuous, or feed mode.The initiators are the free-radical initiators described above, with theazo- initiators being preferred. (Co)polymer molecular masses werecontrolled by varying the monomer-to-CTA molar ratio. Theinitiator-to-CTA molar ratio as at least one-to-one (1:1), and at most1:1000. The initiator-to-CTA molar ratio was generally in an amount suchthat the molar amount of CTA was greater than the molar amount ofinitiator. Preferably, the initiator-to-CTA molar ratio was at least1:1, at most 1:100, and most preferably 1:5 in order to obtain optimalresults. Solution pH was adjusted as necessary to ensure completeionization of the monomers, depending on the charge.

Turning now to an exemplary process according to the invention, thesynthesis begins with the preparation of an aqueous solution of metalsalt or sol, preferably the amount of metal salt or sol being 0.01 wt.%. This metal colloidal solution is then preferentially added to acontainer which has been charged with a dithioester end-capped(co)polymer, as described above. The mixture is mixed, in order toensure homogeneity, and an aqueous solution of reducing agent (1.0 M) isadded slowly. The mixture is then stirred, open to the atmosphere, atroom temperature for a time up to 48 hours. The resultant product isrecovered by centrifugation, or any other suitable means of removing thereaction solution from the product of the invention.

According to the present invention, the reducing agent to be used is aboron hydride compound and/or aluminum hydride compound, or a hydrazinecompound. More specifically, the reducing agent includes but is notlimited to alkali metal borohydrides, alkali earth metal borohydrides,alkali metal aluminum hydrides, dialkylaluminum hydrides and diborane,among others. These may be used singly or two or more of them may beused in a suitable combination. The salt-forming alkali metal in thereducing agent is, for example, sodium, potassium, or lithium and thealkaline earth metal is calcium or magnesium. In consideration of thecase of ease of handling and from other viewpoints, alkali metalborohydrides are preferred, and sodium borohydride is particularlypreferred.

Other preferred reducing agents suitable for use with the presentdisclosure include, but are not limited to: borohydrides such as lithiumborohydride, potassium borohydride, calcium borohydride, magnesiumborohydride, zinc borohydride, aluminum borohydride, lithiumtriethylborohydride [Super Hydride®], lithium dimesitylborohydride,lithium trisiamylborohydride, and sodium cyanoborohydride; lithiumaluminum hydride, alane (AlH₃), alane-N,N-dimethylethylamine complex,L-Selectride™ (lithium tri-sec-butylborohydride), LS-Selectride™(lithium trisiamylborohydride), Red-Al® or Vitride® (sodiumbis(2-methoxyethoxy)aluminum hydride; alkoxyaluminum hydrides such aslithium diethoxyaluminum hydride, lithium trimethoxyaluminum hydride,lithium triethoxyaluminum hydride, lithium tri-t-butyoxyaluminumhydride, and lithium ethoxyaluminum hydride; alkoxy- andalkylborohydrides, such as sodium trimethoxyborohydride and sodiumtriisopropoxyborohydride; boranes, such as diborane, 9-BBN, and AlpineBorane®; aluminum hydride, and diisobutylaluminum hydride (Dibal);hydrazine, and the like. Together with such a reducing agent, a suitableactivator known in the art may be combinedly used for improving thereducing power of the reducing agent. The reducing agent can be used insolid form, in solution with a suitable solvent, or can be attached toan inert support, such as polystyrene, alumina, and the like. Thereducing agent to be used should be mostly soluble in a solvent,particularly in water (e.g., NaBH₄, LiBH₄, or hydrazine), oralternatively in an organic solvent which is miscible with water. Forexample, it is envisioned that that the process of the presentdisclosure can be done using an organic solvent such as tetrahydrofuran(THF) or a THF-water mixture with LiBHEt₃ (Super Hydride®) as thereducing agent.

The amount of the reducing agent is not particularly restricted, but itis preferred to be in an amount such that reducing agent is provided inan amount not less than the stoichiometric amount relative to the amountof the thiocarbonythio compound. For example, the reduction can beeffected using sodium borohydride in an amount of not less than 0.5mole, preferably not less than 1.0 mole, per mole of thethiocarbonylthio compound. From the economic viewpoint, the amount ofreducing agent is not more than 10.0 moles, and preferably not more than2.0 moles per mole of the thiocarbonylthio compound.

In the instance of some of the transition metals included in the presentinvention, and hence included within the present invention, the additionof the reducing agent results in the reduction of the dithioester endgroup of the polymer, resulting in the corresponding thiol functionalityon the (co)polymer with the simultaneous reduction of the metal ion tothe elemental state.

In addition to the above embodiments, the transition metal nanoparticlesor surfaces stabilized or modified by (co)polymers synthesized usingRAFT can be further modified at their terminal functional end groupusing a variety of reaction conditions, such as reagents, time, andtemperature. Recently, there has been growing interest in using variouspolymeric nanoparticles as carrier systems for an increasing number ofcompounds, such as anti-infectious agents, anti-cancer drugs, andantibodies, due in part to the excellent controlled biodegradability andcompatibility properties of these polymers. Such nanoparticles showpromise in the medical field, for example, in that the combinedadvantages of nanoparticles or stabilized surfaces with the advantagesof covalent protein-drug conjugates could enable the modification ofboth body distribution and the enhancement of the cellular uptake of thebound drug (Schäfer, et al., Pharmaceutical Research 1992, Vol. 9, pp.541–546).

Such an embodiment of the present disclosure is illustrated below,wherein a thio functionalized polymer or (co)polymer is grafted to asurface, such as a transition metal nanoparticle, transition metal,silicon wafer, ceramic, biofilm, or the like, wherein the polymer or(co)polymer contains at least one terminal functional group (X) which iscapable of further reaction with an appropriate compound Y. Accordingly,X can be selected from the group consisting of, but not limited to,—NH₂, —NHR, —NR₁R₂, —OH, —CO₂H, —CO₂R, COCl, COBr, COI, NO₂, SHR₁, and—R₁C(O)OC(O)R₂, wherein R, R₁, and R₂ can be alkyl, substituted alkyl,alkenyl, aryl, substituted aryl, aromatic, or heterocyclic, and includesuch compounds as amino acids (all isomeric forms), drugs and drug-likecompounds, peptides, proteins, anhydrides, CTAs, initiators, and anynumber of suitable protecting groups, such as those described in Green,T. W., and Wuts, P. G. M, “Protective Groups in Organic Synthesis”,3^(rd) Ed., John Wiley and Sons, Inc., 1999.

Consequently, and in accordance with the present disclosure, thiolfunctionalized azo-initiators could be attached, or a small moleculethiol containing a functionalizable end group (X) which is capable offurther reaction could be coupled to an appropriate RAFT CTA, allowing avariety of CTAs or initiators to be attached to surfaces.

For example, the transition metal nanoparticles or surfaces of thepresent disclosure can be further modified chemically to enablefunctional groups to be generated on or near the nanoparticle orsurface, which would thereby allow for covalent binding of substrates,such as antibodies, specific peptides, drugs, and the like.Particularly, it is desirable to have accessible thiol groups on or nearthe surface of the nanoparticles in order to achieve the coupling ofvarious compounds to this colloidal system. This in turn can lead to theuse of the nanoparticles and surfaces of the present invention for suchapplications as parenteral administration of medicaments.

A representative example of such a further functionalization of thetransition metal nanoparticles or surfaces of the present invention isillustrated in Scheme 4. Generally, what is shown is the modification ofthe carboxyl structuro-terminal end group of the nanoparticle throughthe introduction of a sulfhydryl group onto the nanoparticle. Thisfunctionality can then be used to couple drugs via thiol-reactivecross-linkers such as maleinimide group containing substrates.

As illustrated in Scheme 4, the modified, sulfhydryl-containingnanoparticles can be prepared using a two-step carbodiimide technique,such as described by Ezpeleta, et al., International Journal ofPharmaceutics 1999, 191, pp. 25–32. Initial activation of the carboxylicacid groups of the nanoparticles by a carbodiimide such as1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDAC) ordiisopropylcarbodlimide (DIC) leads to the formation of an O-isoacylurea(not shown), which is followed by the nucleophilic attack of the amineon the cysteine. This leads to the formation of nanoparticles withexposed, reactive thiol functions near their surface, attached by anamide bond. Consistent with the objectives of the present disclosure,that is to form transition metal nanoparticles in a facile manner usingsolvents such as water in an open-air atmosphere, any non-covalentlyassociated cysteine, as well as the urea derivative by-product of thecarbodiimide generated during the reaction, can be readily eliminatedfrom the nanoparticles by simple washing and drying techniques. Othersuitable methods for the introduction of such thiol functionalities ontonanoparticles include, for example, the coupling of cysteine andcystaminiumdichloride by an aqueous carboduimide reaction, and the useof carbodiimides and cystamine. Since cystamine does no contain directlyavailable sulfhydryl groups, an additional reaction step would berequired in order to reduce the disulfide bonds using a sulfhydrylreducing agent such as dithiotreitol (DDT) ortris(2-carboxyethyl)-phosphine hydrochloride (TCEP).

Further embodiments of the present invention include RAFTpolymerizations of polymers from a surface, such as from ananoparticles, film, or wafer. In such an instance, either the freeradical initiator or the CTA can be attached to the nanoparticle orsurface by any of numerous reactions known in the art. Following suchattachment, the RAFT polymerizations can be carried out in a variety ofsolvents, preferably water or water-solvent emulsion.

The method of using the transition metal-(co)polymer nanoparticles ofthis invention for immobilizing well-defined (co)polymers withα,ω-telechelic functionality to planar supports, immobilizing(co)polymers with derivitizable functionalities, and anchoring a varietyof biological and chemical substances to a solid support, surface ornanoparticle has potential applications in, but is not limited to,microscopy (scanning tunneling, atomic force, angle-dependent x-rayphotoelectron, Auger, and the like), structural analysis, microarrays,dendrimers, proteomics, drug delivery, immunochemistry applications,protein recognition, bioarrays, biosensors and biochips, bioelectronics(e.g. biomimetic or artificial photosynthesis), biorecognition, medicalapplications such as in implants, controlled drug release, artificialskin and joints, artificial organs/tissue engineering and vasculargrafts, biosensors such as bioaffinity sensors, transmembrane sensors,biocatalytic (enzymatic) sensors, and other cell-based sensors, as wellas other biological applications which would be evident to those ofskill in the art. For example, employing hydrophilic (co)polymers in thefield of bioarrays may be advantageous by reducing the extent ofnon-specific, hydrophobic adsorption between spacer molecules separatingthe surface from the bimolecular ligands to which they are attached.

The following examples are included to demonstrate preferred embodimentsof the invention. It should be appreciated by those of skill in the artthat the techniques disclosed in the examples which follow representtechniques discovered by the inventors to function well in the practiceof the invention, and thus can be considered to constitute preferredmodes for its practice. However, those of skill in the art should, inlight of the present disclosure, appreciate that many changes can bemade in the specific embodiments which are disclosed and still obtain alike or similar result without departing from the spirit and scope ofthe invention.

EXAMPLES

Metal compounds used in the present invention are purchased commercially(Sigma-Aldrich Chemical Co.), or synthesized using any number of methodsknown to those of skill in the art. Sources other than commercialsources may be used to obtain the transition metal salts used in thepresent invention. For example, novel, new transition metal salts may beutilized incorporating structural, physical, and chemical propertiesfrom different sources.

Investigation of the structures of the transition-metal stabilizednanoparticles and surfaces formed in the samples can be accomplished byusing a device such as a Zeiss 109-T field emission gun (a 50 kVtransmission electron microscope (TEM) with a point-to-point imageresolution of 0.2 nm), and recording the structural images using aninternal camera, which allows for the subsequent processing andquantitative modeling. Preparation of the TEM specimens is detailedbelow.

General RAFT Solution Polymerization.

Each polymerization was conducted under a nitrogen atmosphere in a 25 mLround-bottomed flask equipped with a magnetic stir bar and sealed with aseptum. 4,4′-azobis(4-cyanopentanoic acid) (Wako Chemical, USA) and4-cyanopentanoic acid dithiobenzoate (prepared by literaturesprocedures, for example as describe in Mitsukami, et al., Macromolecules2001, Vol. 34, pp. 2248–2256) were employed as the initiator and RAFTchain transfer agent (CTA), respectively. The [CTA]: [initiator]remained constant at 5:1 (mole basis). The monomer concentration was 2.0M. The (co)polymers resulting were purified by dialysis againstdeionized water and isolated by lyophilization.

Homopolymers of sodium 4-styrenesulfonate (NaPSS) and(arvinylbenzyl)trimethylammonium chloride (VBTAC) were synthesized inwater (pH 7.0) (PNaPSS: M_(n)=19,800, PDI=1.12; PVBTAC: M_(n)=10,500,PDI=1.06). The homopolymerization of N,N-dimethylacrylamide (DMA) wasconducted in water (pH 7.5) at 70° C. (M_(n)=29,100, PDI=1.18). An ABdiblock copolymer of 3-[2-(N-methylacrylamido)-ethyldimethyl ammonio]propane sulfonate (MAEDAPS) and DMA was prepared by first synthesizingPMAEDAPS in 0.5 M NaBr. The resulting homopolymer was then used as amacro-CTA, with 4,4′-azobis(4-cyanopentanoic acid) as the initiator,allowing the synthesis of a block copolymer in 0.5 M NaBr.(P(MAEDAPS-b-DMA), M_(n)=58,700, PDI=1.19, MAEDAPS : DMA=35:65).

Example 1 Preparation of Polymer-Stabilized Gold Particles

Preparation. Colloidal gold (0.01 wt. % as HAuCl₄, 20 nm) was preparedas previously described, or purchased from a commercial supplier. To atest tube equipped with a magnetic stir bar and containing a dithioesterend-capped polymer (PDMA, PVBTAC, P(MAEDAPS-b-DMA), or PDMA diheaded)(255 mg) was added a solution of colloidal gold (Aldrich, 1.02 g, 0.01wt. %). The mixture was stirred to ensure homogeneity. Aqueous 1MNaBH₄(˜2 mL) was added dropwise and the mixture was allowed to continuestirring at room temperature for 48 hours. An aliquot (0.50 mL) from theresulting solution was removed and centrifuged for 1 hour at 13,000 rpm.The supernatant was removed and the resulting aggregate was rinsed withdeionized water (0.50 mL) with brief agitation. The supernatant wasagain removed and the aggregate was redispersed in deionized water (0.50mL) by agitation for 24 hours.

Characterization. For the observation of the size and distribution ofthe colloidal nanoparticles, a drop of the colloidal solution was placedon a Formvar-coated copper grid and allowed to air-dry. Transmissionelectron microscopy (TEM) was performed as described above, operating atan accelerating voltage of 50 kV. UV-VIS spectroscopy of thenanoparticles was conducted in 1 cm path length cuvettes with a HewlettPackard 8452A diode array spectrophotometer.

Example 2 Preparation of Polymer-Stabilized Silver Particles

Preparation. The colloidal silver solution was prepared in situ from asilver salt (i.e. AgNO₃). The appropriate amount of silver salt wasadded to deionized water (20.0 mL) in order to prepare a 0.01 wt. %solution of the silver ion. The polymer was dissolved in an aliquot ofthis solution and a similar procedure as described above in Example 1was employed in order to prepare the polymer-stabilized colloidalsolution.

Example 3 Preparation of Polymer-Stabilized Platinum Particles

Preparation. The colloidal platinum solution was prepared in situ from aplatinum salt (i.e. Na₂PtCl₆.6H₂O). The appropriate amount of platinumsalt was added to deionized water (20.0 mL) in order to prepare a 0.01wt. % solution of the platinum ion. The polymer was dissolved in analiquot of this solution and a similar procedure as described above inExample 1 was employed in order to prepare the polymer-stabilizedcolloidal solution.

Example 4 Preparation of Polymer-Stabilized Palladium Particles

Preparation. The colloidal palladium solution was prepared in situ froma palladium salt (i.e. Na₂PdCl₆). The appropriate amount of palladiumsalt was added to deionized water (20.0 mL) in order to prepare a 0.01wt. % solution of the palladium ion. The polymer was dissolved in analiquot of this solution and a similar procedure as described above inExample 1 was employed in order to prepare the polymer-stabilizedcolloidal solution.

Example 5 Preparation of Polymer-Stabilized Rhodium Particles

Preparation. The colloidal rhodium solution was prepared in situ from arhodium salt (i.e. Na₃RhCl₆). The appropriate amount of rhodium salt wasadded to deionized water (20.0 mL) in order to prepare a 0.01 wt. %solution of the rhodium ion. The polymer was dissolved in an aliquot ofthis solution and a similar procedure as described above in Example 1was employed in order to prepare the polymer-stabilized colloidalsolution.

Example 6 Preparation of Polymer-Stabilized Ruthenium Particles

Preparation. The colloidal ruthenium solution was prepared in situ froma ruthenium salt (i.e. K₃RuCl₆). The appropriate amount of rutheniumsalt was added to is deionized water (20.0 mL) in order to prepare a0.01 wt. % solution of the ruthenium ion. The polymer was dissolved inan aliquot of this solution and a similar procedure as described abovein Example 1 was employed in order to prepare the polymer-stabilizedcolloidal solution.

Example 7 Preparation of Polymer-Stabilized Osmium Particles

Preparation. The colloidal osmium solution was prepared in situ from aosmium salt (i.e. Na₂OsCl₆.H₂O). The appropriate amount of osmium saltwas added to deionized water (20.0 mL) in order to prepare a 0.01 wt. %solution of the osmium ion. The polymer was dissolved in an aliquot ofthis solution and a similar procedure as described above in Example 1was employed in order to prepare the polymer-stabilized colloidalsolution.

Example 8 Preparation of Polymer-Stabilized Iridium Particles

Preparation. The colloidal iridium solution was prepared in situ from aniridium salt (i.e. Na₂IrCl₆.H₂O). The appropriate amount of iridium saltwas added to deionized water (20.0 mL) in order to prepare a 0.01 wt. %solution of the iridium ion. The polymer was dissolved in an aliquot ofthis solution and a similar procedure as described above in Example 1was employed in order to prepare the polymer-stabilized colloidalsolution.

Example 9 Immobilization of RAFT-prepared (Co)polymers onto Gold Film

Gold-coated glass slides (1 cm×1 cm×1000 Å) were obtained from EMFCorporation (Ithaca, N.Y.). Immediately prior to use, the slides wereimmersed for 2 minutes in freshly prepared “piranha” solution (70/30,v/v, concentrated H₂SO₄/30% H₂O₂) at 80° C., rinsed with deionizedwater, and dried under a nitrogen atmosphere. The surface modificationreactions involved dropwise addition of aqueous NaBH₄ (0.5 mL, 1.0 M) toa solution of dithioester end-capped polymer (PDMA, PVBTAC,P(MAEDAPS-b-DMA), or PDMA diheaded) in deionized water (5.0 mL, 0.1 mM).The gold-coated slides were placed in the solution of newly-formedthiols for 48 hours. The slides were then removed from the supernatant,rinsed by constant agitation in deionized water for 48 h, and driedunder a nitrogen atmosphere.

Characterization: Tapping mode atomic force microscopy (AFM) images werecollected using a Digital Instruments 3000 scanning probe microscope.Each slide was examined at a minimum of three different locations on thesample surface.

Surface hydrophobicity was examined by performing water contact anglemeasurements with a First Ten Angstroms FTÅ 200 Dynamic Contact AngleAnalyzer. Three sets of contact angle measurements were collected, usinga 10 μl drop size of deionized, distilled water. Between measurements,samples were dried in an oven at 55° C. for 10 minutes.

The results of the water contact angle measurements are shown in Table2. All of the films demonstrated reduced contact angles as compared tothe unmodified gold, thereby suggesting a surface transition to a morehydrophilic state. The contact angle obtained for the unmodified goldcontaining adventitious, nonpolar material is similar to that reportedin the art. This reduction in contact angle following the polymerimmobilization procedures of the present disclosure is expected owing tothe extremely hydrophilic nature of the (co)polymers employed.

TABLE 2 Water contact angle measurements obtained for gold filmsmodified with various (co)polymers. Modifying (co)polymer Water ContactAngle (deg) No Polymer (control) 75.9° NaPSS 67.3° PDMA 30.5°P(MAEDAPS-b-DMA) 29.1° PMAEDAPS 41.5° PVBTAC 41.4°

Interestingly, the contact angle for the P(MAEDAPS-b-DMA) sample (29.1°)was nearly identical to that of the PDMA-modified gold (30.5°) andsimilar to the contact angle reported by Baum et al. (Macromolecules2002, Vol. 35, pp. 610–615) for PDMA brushes grafted from a silicatesurface (33°). This result was striking because the dithioester residesat the terminus of the DMA block, and following attachment, the outerblock is expected to be MAEDAPS. However, due to the similarity of thecontact angles observed for the block copolymer and PDMA samples, whilenot intending to be held to one particular hypothesis, it seems likelythat the DMA block was exposed.

In order to gain further insight, the contact angle was determined for agold film modified with MAEDPAS homopolymer. PMAEDAPS is derived from asulfobetaine monomer that contains both positive and negative charges onthe same repeat unit. As a result of the electrostatic interactionsbetween the opposite charges, polybetaines are not soluble in deionizedwater but are soluble in aqueous salt solutions. The water contact anglefor the gold modified with PMAEDAPS was determined to be 41.5°,indicating the surface was more hydrophobic than the gold modified withthe block copolymer. This result, coupled with the similarity observedbetween the contact angles of the PDMA and the P(MAEDAPS-b-DMA) samples,suggest the relatively hydrophobic MAEDAPS block causes the blockcopolymer to adopt a conformation such that the more hydrophilic DMAblock is exposed to the aqueous environment. Rearrangement of the blocksmost likely occurred when the sample was treated with deionized waterduring the rinsing step that immediately followed the immobilizationprocedure.

Attenuated total reflectance Fourier transform infrared (ATR FT-IR)spectra were obtained with a Digilab FTS-6000 FT-IR single-beamspectrometer set at a 4 cm⁻¹ resolution. A 45° face angle Ge crystalwith 50×20×3 mm dimensions was used. This configuration allows theanalysis of the film-air interface from monolayer levels toapproximately 0.2 μm from the surface. Each spectrum represents 5000co-added scans ratioed to 5000 co-added reference scans that werecollected using an empty ATR cell. All spectra were corrected forspectral distortions and optical effects using Q-ATR software. Molecularweights and polydispersities were determined by aqueous size exclusionchromatography.

Prophetic Examples

The following prophetic examples are meant to describe alternativeprocedures and embodiments of the present disclosure which have beenenvisioned by the inventors.

Prophetic Example 1 Preparation of Polymer-Stabilized Gold ParticlesUsing LiBHEt₃ (Super Hydride®) as the Reducing Agent

Colloidal gold (0.01 wt. % as HAuCl₄, 20 nm) is prepared as previouslydescribed, or purchased from a commercial supplier. To a test tubeequipped with a magnetic stir bar and containing a dithioesterend-capped polymer (PDMA, PVBTAC, P(MAEDAPS-b-DMA), or PDMA diheaded)(255 mg) is added a solution of colloidal gold (Aldrich, 1.02 g, 0.01wt. %). The mixture is stirred to ensure homogeneity. A 1.0 M solutionof LiBHEt₃(˜2 mL) in THF is added dropwise and the mixture is allowed tocontinue stirring at room temperature for 48 hours. An aliquot (0.50 mL)from the resulting solution is removed and centrifuged for 1 hour at˜13,000 rpm. The supernatant is removed and the resulting aggregate isrinsed with deionized water (0.50 mL) with brief agitation. Thesupernatant is again removed and the aggregate is redispersed indeionized water (0.50 mL) by agitation for 24 hours. Analysis of thesize and distribution of the colloidal nanoparticles by TEM and UV-VISspectroscopy gives results similar to those described in the examplesabove.

Prophetic Example 2 Preparation of Polymer-Stabilized Iridium ParticlesUsing Hydrazine as the Reducing Agent

Colloidal iridium (0.01 wt. % as Na₂IrCl₆.6H₂O, 20 nm) is prepared aspreviously described, or purchased from a commercial supplier. To a testtube equipped with a magnetic stir bar and containing a dithioesterend-capped polymer (PDMA, PVBTAC, P(MAEDAPS-b-DMA), or PDMA diheaded)(255 mg) is added a solution of colloidal iridium (Aldrich, 0.01 wt. %).The mixture is stirred to ensure homogeneity. A 1.0 M solution ofhydrazine (H₂NNH₂.H₂O, ˜2 mL) in water, THF, or a water-THF mixture isadded dropwise and the mixture is allowed to continue stirring at roomtemperature for 48 hours. An aliquot (0.50 mL) from the resultingsolution is removed and centrifuged for 1 hour at 13,000 rpm. Thesupernatant is removed and the resulting aggregate is rinsed withdeionized water (0.50 mL) with brief agitation. The supernatant is againremoved and the aggregate is redispersed in deionized water (0.50 mL) byagitation for 24 hours. Analysis of the size and distribution of thecolloidal nanoparticles by TEM and UV-VIS spectroscopy gives resultssimilar to those described in the examples above.

Prophetic Example 3 Immobilization of RAFT-prepared (Co)polymers ontoSilicon Wafers

Preparation of substrate: A freshly cleaned (‘piranha” solution) siliconwafer is placed into a solution of a silane (either a monofunctional ortrifunctional chlorosilane) in an appropriate solvent, such as toluene.The reaction is allowed to react at ambient temperature forapproximately 12 h under an inert atmosphere. The modified substrate isthen rinsed with an organic solvent and dried.

Surface-Initiated RAFT Polymerization: A reaction vessel containingfunctionalized silcon substrate is charged with monomer, appropriatesolvent or solvents, free-radical initiator (e.g. AIBN or other suitableinitiator) and/or a dithio CTA (e.g, DTBA). The solution is degassed,then heated to the appropriate temperature, depending upon thereactants, for an appropriate time period. Following the completion ofpolymerization, the modified substrate is extracted, washed and dried(e.g. vacuum). Characterization is by any number of appropriatetechniques, such as ¹H-NMR, FTIR-ATR, TGA, DSC and XPS.

Prophetic Example 4 Thiolation of Transition Metal Nanoparticles UsingCysteine (c.f., Scheme 3)

Preparation of transition metal nanoparticles: Nanoparticles or surfacesare prepared according the examples given above, e.g. examples 1–9,using PDMA, NaPSS, PVBTAC or P(MAEDAPS-b-DMA) as the (co)polymers.Characterization is by any number of methods, such as TEM or photoncorrelation spectroscopy.

Introduction of thiol functionality: The carboxylic groups on thetransition metal nanoparticles (or surface) is activated in anappropriate solution (e.g., water, organic solvent, phosphate buffer,etc.) by dropwise addition of a solution of EDAC. The mixture isincubated at room temperature for a time sufficient to allow completeactivation of a majority of the carboxyl groups. The unreacted EDAC isthen removed, the nanoparticles (or modified surface) washed briefly,and then resuspended in solution. Cysteine hydrochloride (L-, D-, or aracemic mixture) is made up in solution, and added to the suspensioncontaining the activated nanoparticles. The mixture is shaken oragitated gently at room temperature for a time necessary to allow thereaction to go to completion. The conjugated nanoparticles are washedusing any appropriate means (e.g., centrifugation) in order to removeany cysteine remaining. Analysis of the thiol functionalized productsincludes the use of Ellman's reagent to determine the number of thiolgroups on the nanoparticle surface.

The colloidal metal particles and surfaces, as used herein, are preparedfollowing known art procedures, or purchased commercially. The colloidalmetal particles and surfaces may then be attached, and consequentlystabilized, to (co)polymers in aqueous solution which have been preparedby the RAFT process. It has been shown (U.S. Pat. No. 4,775,636;Moeremans, et al.) that colloidal metal particles which are attached tobinding agents (proteins, for example) will accumulate at specificbinding sites and hence become visible as the color characteristics ofthe colloidal metal particles used, e.g. from pink to dark red color, inthe case of gold. This signal can be detected by eye, or by using any ofa number of known spectrophotometric techniques. Similarly, thetransition metal nanoparticles and surfaces of this invention which aremodified by RAFT synthesized (co)polymers exhibited similarcharacteristics. These results are shown in Table 3.

TABLE 3 Visible color characteristics of the colloidal transition metalnanoparticles of examples 1–8. Metal Sol'n color Sol'n color Sol'ncolor, (Salt Used) Polymer before reduction after reduction 48 h Au PDMARed Purple Pink HAuCl₄.H₂O PVBTAC Purple Purple P(MAEDAPS-b-DMA) PurplePurple PDMA Diheaded Pink Pale pink Control (no polymer) w.w. Slightppt. Ag PDMA w.w. Dark w.w., slight ppt. AgNO₃ green/brown PVBTACGreen/grey Amber P(MAEDAPS-b-DMA) v. dark brown Pale brown PDMA Diheaded— — Control (no polymer) Black ppt. Black ppt. Pt PDMA w.w. w.w. w.w.Na₂PtCl₆.6H₂O PVBTAC w.w. Pale brown P(MAEDAPS-b-DMA) w.w. w.w. PDMADiheaded — — Control (no polymer) w.w. Black ppt. Pd PDMA Golden Palebrown w.w. Na₂PdCl₆.4H₂O PVBTAC orange Orange/brown w.w.P(MAEDAPS-b-DMA) Orange/brown w.w. PDMA Diheaded — — Control (nopolymer) Black ppt. Black ppt. Ir PDMA Dark w.w. w.w. Na₂IrCl₆.6H₂OPVBTAC gold/ w.w. Clear pale yellow brown, slight ppt. P(MAEDAPS-b-DMA)w.w. w.w. PDMA Diheaded w.w. w.w. Control (no polymer) w.w. v. slightppt. Rh PDMA w.w. w.w. Grey/black, v. NaRhCl₆ slight ppt. PVBTAC w.w.Clear gold, v. slight ppt. P(MAEDDAPS-b-DMA) Yellow/brown Clear brown,v. slight ppt. PDMA Diheaded Yellow/brown w.w., v. slight ppt. Control(no polymer) Black ppt. Black ppt. Os PDMA Pale w.w. w.w. Na₂OsCl₆.H₂OPVBTAC yellow/green w.w. w.w., v. slight ppt. PDMA Diheaded w.w. w.w.Control (no polymer) w.w. v. slight ppt. Ru PDMA Pale v. pale yellowClear pale K₃RuCl₆ brown/green brown PVBTAC v. pale yellow Clear palebrown P(MAEDAPS-b-DMA) v. pale yellow Clear pale brown PDMA Diheaded v.pale yellow Clear pale brown Control (no polymer) Black ppt. Black ppt.w.w. = water white; v = very; ppt. = precipitate.

All of the processes disclosed and claimed herein can be made andexecuted without undue experimentation in light of the presentdisclosure. While the compositions and methods of this invention havebeen described in terms of preferred embodiments, it will be apparent tothose of skill in the art that variations may be applied to theprocesses and in the steps or in the sequence of steps of the methodsdescribed herein without departing from the concept, spirit and scope ofthe invention. More specifically, it will be apparent that certainagents which are chemically related may be substituted for the agentsdescribed herein while the same or similar results would be achieved.All such similar substitutes and modifications apparent to those skilledin the art are deemed to be within the spirit, scope and concept of theinvention.

1. A method of producing transition metal surfaces modified by(co)polymers synthesized using Reversible Addition-Fragmentation chainTransfer (RAFT), comprising: forming a thiocarbonylthio end-capped(co)polymer by reacting a polymerizable monomer or co-monomers with afree radical source and a thiocarbonylthio chain transfer agent (CTA)using the RAFT method in a solvent solution; contacting the transitionmetal surface with the end-capped (co)polymer; and introducing areducing agent into the solution of end-capped (co)polymer andtransition metal surface to simultaneously reduce the thiocarbonylthioend-capped (co)polymer and the transition metal surface so as to anchorthe (co)polymer directly to the transition metal surface.
 2. The methodaccording to claim 1, wherein the solvent comprises water.
 3. The methodaccording to claim 1, wherein the forming and introducing steps areperformed open to the atmosphere.
 4. The method according to claim 1,wherein the free radical source is a free radical source selected fromthe group consisting of azo-compounds, peroxides, redox systems, andreducing sugars.
 5. The method according to claim 1, wherein the CTA isa thiocarbonylthio compound selected from the group consisting ofdithioesters, xanthates, dithiocarbamates, and trithiocarbonates.
 6. Themethod according to claim 1, wherein the surface is selected from thegroup consisting of nanoparticles, films, salts, colloids, sols, andwafers.
 7. The method according to claim 1, wherein the reducing agentincludes at least one of the compounds selected from the groupconsisting of NaBH₄, KBH₄, LiBH₄, Ca(BH₄)₂, Mg(BH₄)₂, Zn(BH₄)₂,Al(BH₄)₃, LiAlH₄, NaBH₃CN, H₂NNH₂, B₂H₆, 9-BNN, lithiumtri-sec-butylborohydride, lithium trisiamylborohydride, LiAlH(OtBu)₃,LiAlH(OMe)₃, LiAlH(OEt)₃, Li(mesityl)₂BH₂, Li(siamyl)₃BH, NaBH(OMe)₃,and NaBH(OiPr)₃.
 8. The method of claim 1 wherein the (co)polymer is athiocarbonylthio end-capped (co)polymer and wherein the surfacecomprises metal precursor colloidal nanoparticles in solution.
 9. Themethod of claim 1 wherein the end-capped (co)polymer is athiocarbonylthio end-capped (co)polymer and the method further comprisesallowing the solution and surface to remain in contact for a set periodof time to stabilize and form a (co)polymer-modified transition metalsurface.